I. Field of the Invention
This invention relates to an improvement in a method for converting cyclo-olefins to nitrosochlorides, particularly for converting cyclo-olefins to the corresponding chloronitrosodimers using sulfur dioxide as solvent. These dimers are useful as monomer precursors for polyamides or in a variety of other applications. In particular, the 2-chloro-1-nitrosocyclohexane dimer is a valuable intermediate in the synthetic production of lysine.
II. Description of the Prior Art
The reaction of nitrosyl chloride with olefins has been studied intensively and has played a major role in the structure determination and identification of terpenes. Depending on experimental conditions and olefin structures, the reaction leads to 2-chloro-1-nitrosoalkane dimers, chloro-oximes, chloronitro compounds, dichloro compounds, dichloronitroso compounds and nitro-nitroso compounds.
More specifically, the dimer derived from cyclohexene, 2-chloro-1-nitroso-cyclohexane dimer (CNCD), was first reported by Bayer in 1894. In 1948, R. K. Allison disclosed in U.S. Pat. No. 2,485,180 a significant improvement in the synthesis of CNCD and terpene derived dimers by using liquid SO.sub.2 as the reaction solvent at preferred temperatures between -40.degree. and -60.degree.C. By using molar ratios of NOCl to olefin within the ranges of 0.892 to 1.2, relatively low yields (i.e. less than 75%) of dimer, were obtained with the reported poorest yields at molar ratios less than 1.0, and with the remainder of the reaction mixture consisting essentially of undesired addition by-products.
Experimental evidence in the literature indicates that the chloro-nitroso dimer obtained from liquid SO.sub.2 solvent is the result of a trans addition of NOCl to the double bond and the structure has accordingly been assigned trans -2,2'-dichlorotrans-azodioxycyclohexane. Further evidence indicates that the Cl--NO interaction is strong in the diaxial form and dipole repulsion equally strong in the equatorial form so as to imply the presence of the following three conformers: ##SPC1##
Allison's work has been repeated or modified by Ohno et al. as shown in Tetrahedron, Letters 43, 4047-4052, 1965 and by Yoshida in Tetrahedron, Letters 32, 2763-2766, 1965 wherein dimer yields remain substantially low, i.e. in the range of 60-80 mole percent.